The brake assemblies of large industrial utility vehicles such as dump trucks, tractor and trailer rigs, and the like are subjected to extreme forces during braking operations. Accordingly, brake assemblies and the components therefor are specially designed to withstand the high heat and stresses created during braking. A problem that remains, however, is rusting and corrosion of the brake shoe. Such corrosion usually is due to the collection of moisture on the brake shoe, including on the brake shoe table, and the presence of moisture can lead to premature failure of the brake shoe, necessitating its removal and replacement.
Brake shoes typically are unprotected from below the vehicle. As a result, spray from the road surface tends to be directed toward and collected on brake shoes, causing the brake shoes to rust. This problem is especially prevalent near the sea shore where salt is present on the roads and in areas of abundant rain and snow falls. The problem is further compounded by salt and other corrosive elements often applied to roads in areas of heavy snow falls to melt snow and ice.
Additionally, frictional brake liners for brake shoe assemblies were formerly made of asbestos, which provided a relatively high degree of flexibility to the brake liners. The flexibility of the liners enabled the brake liners to bend and tightly conform to the curvature of the brake shoe table to create a tight sealing contact between the brake liners and the brake shoe table. The tight fit between the brake liner and the table of the brake shoe avoided the presence of gaps being formed between the brake liner and the brake shoe table and therefore avoided moisture being collected between the brake liner and the brake shoe table. However, due to health and safety concerns, the use of asbestos for such applications is now avoided.
The frictional brake liners that are now being used typically are formed from high strength substantially rigid materials, which do not have the flexibility of the old asbestos brake liners. As a result of being stiff, the newer conventional brake liners do not always accurately mate with the brake shoe tables as well as did the old asbestos brake liners. Accordingly, gaps or cracks are often formed between the brake liners and the brake shoe tables, which enables moisture to accumulate between the liner and the table of the brake shoe.
To correct these gaps and provide a tighter sealing fit between the brake liners and brake shoe tables, most brake manufacturers typically rework or "coin" the tables of their brake shoes after manufacture to achieve a radius that better fits the radius of the brake liner. Such a process increases the cost of the brake shoes and does not completely eliminate the gaps or cracks between the brake liners and the brake shoe tables. As a result, moisture is still able to reach the brake shoe table of some brake shoes.
Further, the methods of attachment of the brake liners to the brake shoes have contributed to the contact of moisture with the brake shoe tables. In the past, rivets or bolts have been used to attach the brake liners to the brake shoe table. Such fasteners require holes to be drilled through the brake liner and through the brake shoe table. These fastener holes enable the passage of moisture through the brake liner and brake shoe.
Recently, heat induced epoxies have been utilized to attach the brake liner to the brake shoe table. The epoxies are applied to the brake shoe table as a molten adhesive, filling any gaps between the brake shoe table and the brake liner. The epoxies are then allowed to cool and set, forming a rigid non-fluid attachment between the brake liner and the brake shoe table. However, once these adhesives dry, they form a hard, solid layer which tends to crack and break over time under high heat and stress, thus forming gaps and cracks between the brake liner and the brake shoe table. As a result, moisture can still eventually pass to the brake shoe table through the cracks in the epoxy.
Accordingly, it can be seen that it would be desirable to provide a brake shoe assembly having a means for sealing the brake shoe against contact with or the passage therethrough of moisture, to prevent the rusting and corrosion of the brake shoe.